I've got the controller and tower working and I can keep the mash at a constant temperature. The temperature will show a variance of +/-~5 to 10 percent of desired temperature on the controller. But I have a thermometer in the mash and the temperature is steady throughout the mash. Remember the system is pulling wort from the bottom of the tun and as the flame was on, it is hot. This thing works great and if I could get the controller to talk to the computer, it would be near perfect.